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<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <meta http-equiv="X-UA-Compatible" content="ie=edge" />
  <title>Document</title>
  <style>
    div{
      margin: 200px auto;
      width: 400px;
      height: 120px;
      font-size: 50px;
    }
    span {
      display: inline-block;
      width: 100px;
      height: 100px;
      background-color: #000;
      color: #fff;
      font-size: 50px;
      text-align: center;
      line-height: 100px;
    }
  </style>
</head>

<body>
  <div>
    <span id="hour">01</span> : <span id="minute">03</span> : <span id="second">10</span>
  </div>

  <script>
    /*
      思路:
      设置一个计时器,间隔时间1秒钟,
      获取时分秒span标签的文本, 秒--, 重新赋值给span标签
    */









  </script>
</body>

</html>